Weird cast to lens - any advice ?

Astro-Baby · 05-05-2019, 02:07 AM

A local charity shop asked my opinion on a lens recently - its for an old Minolta MC mount. I have to confess I seldom see lenses that are faulty - in years of photography I have never seen many problems and usually they are pretty obvious (the glass is busted or the focus is locked up). In years of snapping I have never seen any of the problems that seem so prevalent these days like fungus, balsam seperation, haze etc and that includes my astronomy gear which has to face tougher conditions than the average camera lens.

Anyway - down to brass tacks - they asked my opinion as I go in there quite a bit and I haven't a clue so perhaps someone with knowledge can advise -

The lens looks clear under artificial light - a few scratches but nothing to worry about. Then I looked at the lens again in daylight and around the edge of the front element as you turn it to light there is what looks like a ragged purple ring. The only way I could describe it is is looks like the lens originally had a deep purple coating but across the lens surface it has been washed off except at the lens edges - it extends about 2-4mm away from the barrel edge. But whatever this is is not on the front of the lens but on its rear surface and probably between the front element and the 2nd air spaced element (thats an assumption). Its definitely on the lens rather than a light reflection as the ragged edges are quite different shapes and they stay in place as the lens moves so its not some sort of ghosting.

I did a bit of fast reading and it doesn't look like any pics I have seen of balsam separation and its certainly not fungus - my only thought is its oil thats leaked out from the focus threads but it seems way too far up the lens for that. I tried to get a pic of it but its impossible to photograph well. On a pic it just looks like refraction off the lens coating or natural flare - its very deep hued in color.

Any ideas ?

**Kerrowdown** · 05-05-2019, 04:01 AM

Originally posted by Astro-Baby

Weird cast to lens

Does it show up in the final imagery?

If not I wouldn't worry too much, it sounds like from the way you describe it to be... perhaps some over zealous cleaning that has had an affect on the external multi lens coating, if that's in fact possible.

Just keep an eye on it to see if it changes in any way with time.

Astro-Baby · 05-05-2019, 04:36 AM

No way of knowing if it would show - I was only looking at it for the guy in the shop to be helpful. I don't think it could be overzealous cleaning as the purple stuff is on the inside of the lens - you could see it if you wiped a finger that the finger grease is on the outside but whatever this stuff is is the other side of the glass. I was just curious as I have never seen. lens do this - to be fair my experience isn't that great because until taking up film again I had never seen so many lenses in such poor shape. Its sad really to see hardware that cost a bomb in the day being left to rot. Sighs !

**Kerrowdown** · 05-05-2019, 05:23 AM

Originally posted by Astro-Baby

purple stuff is on the inside of the lens

Oops missed that bit on the original post...

In that case... unless it's a legendary lens at a ridiculous price, IMHO I'd give it a miss.

Wasp · 05-05-2019, 11:48 AM

Wild guess from my side. Perhaps someone dismantled it and put it together the wrong way, i.e. with one element reversed. This can lead to weird things. I can remember reading that on these pages a while back.

Not a Number · 05-05-2019, 12:40 PM

Without actually seeing the lens it is difficult to say what is going on. It could be separation. If it is indeed on the inner surfaces it could be someone cleaned the lens with copious amounts of some solvent that got into the lens. Perhaps someone poured lighter fluid into the helical threads or onto the diaphragm to loosen either up.

The coating on Minolta's 50/58mm f1.2 and f1.4 tend to have an overall amber hue. The rest of Minolta lenses tend to have a bluish-purplish hue.

kypfer · 05-05-2019, 02:18 PM

I've got several lenses with similar symptoms, to a greater or lesser extent. Disassembly, where possible, has always shown the cause to be partial separation of two cemented elements. The net result on the final image ... possibly a slight reduction in contrast, certainly nothing to worry about in this day and age of digital manipulation. Remember, the effect you're seeing is a reflection, the transmission is quite different and probably only noticeable in a side-by-side comparison of two otherwise identical lenses!

YMMV

**pentaxus** · 05-05-2019, 10:28 PM

Some early Minolta lenses have a soft coating on internal elements.It cannot be cleaned. Any cleaning removes the coating. That may be what you are seeing.

Astro-Baby · 05-06-2019, 03:06 AM

Kypfer ..good call on the reflection versus transmission. I hadnt thought of that. Something to consider when I am shopping.

Astro-Baby · 05-10-2019, 10:44 AM

Well I ended up buying the lens because I suffer from terminal OCD, and Gear Acquisition Syndrome and I figured £5 would be ok and saw it as a learning exercise. The problem was that some clown had put too much cleaner on it and the liquid had leaked behind the front element. Its a 55mm Rokkor 1.7 (Second Series) and a bit of reading showed the lens has a massive air gap behind the front element - I guessed (correctly as it turned out) that if I could get the element out it would clean up ok and it did. Now I have a 50mm to go with the SRT101 I have.

Anyway thats why you should always put lens cleaner on a cloth and then clean - not spray onto the lens.

As ever thanks for all your help/advice.

05-05-2019, 02:07 AM	#1
Astro-Baby Veteran Member Join Date: Nov 2018 Location: Reigate, Surrey Posts: 764	Weird cast to lens - any advice ? A local charity shop asked my opinion on a lens recently - its for an old Minolta MC mount. I have to confess I seldom see lenses that are faulty - in years of photography I have never seen many problems and usually they are pretty obvious (the glass is busted or the focus is locked up). In years of snapping I have never seen any of the problems that seem so prevalent these days like fungus, balsam seperation, haze etc and that includes my astronomy gear which has to face tougher conditions than the average camera lens. Anyway - down to brass tacks - they asked my opinion as I go in there quite a bit and I haven't a clue so perhaps someone with knowledge can advise - The lens looks clear under artificial light - a few scratches but nothing to worry about. Then I looked at the lens again in daylight and around the edge of the front element as you turn it to light there is what looks like a ragged purple ring. The only way I could describe it is is looks like the lens originally had a deep purple coating but across the lens surface it has been washed off except at the lens edges - it extends about 2-4mm away from the barrel edge. But whatever this is is not on the front of the lens but on its rear surface and probably between the front element and the 2nd air spaced element (thats an assumption). Its definitely on the lens rather than a light reflection as the ragged edges are quite different shapes and they stay in place as the lens moves so its not some sort of ghosting. I did a bit of fast reading and it doesn't look like any pics I have seen of balsam separation and its certainly not fungus - my only thought is its oil thats leaked out from the focus threads but it seems way too far up the lens for that. I tried to get a pic of it but its impossible to photograph well. On a pic it just looks like refraction off the lens coating or natural flare - its very deep hued in color. Any ideas ?

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05-05-2019, 04:01 AM	#2
Kerrowdown PEG Moderator Join Date: Aug 2008 Location: Highlands of Scotland... "Hold Infinity in the palm of your hand" - William Blake Photos: Gallery Posts: 57,816	Originally posted by Astro-Baby Weird cast to lens Does it show up in the final imagery? If not I wouldn't worry too much, it sounds like from the way you describe it to be... perhaps some over zealous cleaning that has had an affect on the external multi lens coating, if that's in fact possible. Just keep an eye on it to see if it changes in any way with time.

05-05-2019, 04:36 AM	#3
Astro-Baby Veteran Member Join Date: Nov 2018 Location: Reigate, Surrey Posts: 764 Original Poster	No way of knowing if it would show - I was only looking at it for the guy in the shop to be helpful. I don't think it could be overzealous cleaning as the purple stuff is on the inside of the lens - you could see it if you wiped a finger that the finger grease is on the outside but whatever this stuff is is the other side of the glass. I was just curious as I have never seen. lens do this - to be fair my experience isn't that great because until taking up film again I had never seen so many lenses in such poor shape. Its sad really to see hardware that cost a bomb in the day being left to rot. Sighs !

05-05-2019, 05:23 AM	#4
Kerrowdown PEG Moderator Join Date: Aug 2008 Location: Highlands of Scotland... "Hold Infinity in the palm of your hand" - William Blake Photos: Gallery Posts: 57,816	Originally posted by Astro-Baby purple stuff is on the inside of the lens Oops missed that bit on the original post... In that case... unless it's a legendary lens at a ridiculous price, IMHO I'd give it a miss.

05-05-2019, 11:48 AM	#5
Wasp Pentaxian Join Date: Mar 2017 Location: Pretoria Photos: Gallery Posts: 4,660	Wild guess from my side. Perhaps someone dismantled it and put it together the wrong way, i.e. with one element reversed. This can lead to weird things. I can remember reading that on these pages a while back.

05-05-2019, 12:40 PM	#6
Not a Number Moderator Join Date: Mar 2012 Location: Venice, CA Posts: 10,526	Without actually seeing the lens it is difficult to say what is going on. It could be separation. If it is indeed on the inner surfaces it could be someone cleaned the lens with copious amounts of some solvent that got into the lens. Perhaps someone poured lighter fluid into the helical threads or onto the diaphragm to loosen either up. The coating on Minolta's 50/58mm f1.2 and f1.4 tend to have an overall amber hue. The rest of Minolta lenses tend to have a bluish-purplish hue.

05-05-2019, 02:18 PM	#7
kypfer Pentaxian Join Date: Jan 2018 Location: Jersey C.I. Posts: 3,593	I've got several lenses with similar symptoms, to a greater or lesser extent. Disassembly, where possible, has always shown the cause to be partial separation of two cemented elements. The net result on the final image ... possibly a slight reduction in contrast, certainly nothing to worry about in this day and age of digital manipulation. Remember, the effect you're seeing is a reflection, the transmission is quite different and probably only noticeable in a side-by-side comparison of two otherwise identical lenses! YMMV

05-05-2019, 10:28 PM	#8
pentaxus Site Supporter Join Date: Jun 2010 Location: Central Coast, CA Posts: 1,313	Some early Minolta lenses have a soft coating on internal elements.It cannot be cleaned. Any cleaning removes the coating. That may be what you are seeing.

05-06-2019, 03:06 AM	#9
Astro-Baby Veteran Member Join Date: Nov 2018 Location: Reigate, Surrey Posts: 764 Original Poster	Kypfer ..good call on the reflection versus transmission. I hadnt thought of that. Something to consider when I am shopping.

05-10-2019, 10:44 AM	#10
Astro-Baby Veteran Member Join Date: Nov 2018 Location: Reigate, Surrey Posts: 764 Original Poster	Well I ended up buying the lens because I suffer from terminal OCD, and Gear Acquisition Syndrome and I figured £5 would be ok and saw it as a learning exercise. The problem was that some clown had put too much cleaner on it and the liquid had leaked behind the front element. Its a 55mm Rokkor 1.7 (Second Series) and a bit of reading showed the lens has a massive air gap behind the front element - I guessed (correctly as it turned out) that if I could get the element out it would clean up ok and it did. Now I have a 50mm to go with the SRT101 I have. Anyway thats why you should always put lens cleaner on a cloth and then clean - not spray onto the lens. As ever thanks for all your help/advice.